JPH07131616A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain high-definition image while keeping non-magnification at all times without being affected by a temperature change by controlling a write clock frequency corresponding to the change of scanning speed. CONSTITUTION:Scanning time (count number) T1 between a first laser beam detection sensor 105 and a second laser beam detection sensor 106 is measured. Next, a control circuit reads the count number latched by setting the OC signal of a flip-flop from 'H' to 'L', decides whether any error is generated during a magnification correcting operation or not, executes error processing when the error is detected, reports the contents of the generated error to a control part of a higher order than this operation as a message, sets the prescribed write clock frequency and finishes the processing. Thus, the magnification is automatically corrected corresponding to the change of optical characteristics caused by the environmental change of a scanning optical system for converging the scanned laser beams onto the image recording surface of a photosensitive drum 103 and forming images.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for writing image information on a photosensitive member by using laser light, and more specifically, at least two laser light detecting means are used to detect the laser light. One of the image forming apparatuses measures the count number of a predetermined clock from the time when one of the laser light detecting means detects the laser light by the other laser light detecting means, and corrects the write clock frequency based on the measured value. Regarding

[0002]

2. Description of the Related Art As a conventional image forming apparatus, there is an image forming apparatus which writes image information on a photosensitive member using laser light. In recent years, in such an image forming apparatus, a plastic lens has been used for the purpose of cost reduction and weight reduction.

Further, with the spread of image forming apparatuses such as laser printers, laser fax machines, and laser copying machines, and the widespread use thereof, the demand for equal-magnification (precision of zooming) of images is further increased. ing.

[0004]

However, in the image forming apparatus using the conventional plastic lens, although cost reduction and weight reduction can be achieved, due to the change of the environmental temperature, the change of the in-machine temperature, etc., Since the state of the plastic lens changes, the scanning position on the image surface of the photoconductor changes, which causes a magnification error in the main scanning direction, which makes it impossible to obtain a high-quality image. In particular,
In a copying machine that requires accurate reduction and the like, there has been a problem because the image equal magnification (precision of zooming) is reduced.

The present invention has been made in view of the above, and is of a high quality which always maintains equal magnification (precision of zooming) without being affected by a change in scanning speed due to a change in temperature. The purpose is to obtain an image.

[0006]

In order to achieve the above object, the present invention detects a laser beam moving in the main scanning direction in an image forming apparatus for writing image information on a photoconductor using the laser beam. A plurality of laser light detecting means, and measures the count number of a predetermined clock from the time when one of the plurality of laser light detecting means detects the laser light until the other laser light detecting means detects the laser light. Comparing the measured count number with the reference count number that has been set by the measurement means, and corrects the write clock frequency so that the measured count number matches or substantially matches the reference count number. The present invention provides an image forming apparatus including a writing frequency correction unit.

The reference count number is determined by using a timing signal having a certain constant frequency, after the laser light is detected by one of the plurality of laser light detecting means by the measuring means and then by another laser light detecting means. Is to measure and set the count number until the laser detects the laser light. Further, the certain constant frequency is a certain constant write clock frequency. Further, it is assumed that the certain constant write clock frequency is the basic write clock frequency before correction.

Further, it is assumed that the reference count number is the count number measured by the measuring means when the write clock is initially adjusted.

Further, the write frequency correction means adjusts the write clock frequency to a predetermined reference write clock frequency or initially adjusts the write clock when an error occurs during the write clock frequency correction operation. The write clock frequency set at the time of performing or the write clock frequency corrected immediately before the error occurs is set, and the correction operation is ended.

A signal obtained from at least one of the plurality of laser light detecting means is used as a laser light scanning synchronization signal.

Further, the write frequency correction means executes the correction of the write clock frequency when the start button of the image forming operation is pressed.

Further, the write frequency correction means executes correction of the write clock frequency between frames during continuous recording.

Further, when the writing frequency correcting means does not measure the count number between the laser light detecting means, the laser is not emitted at a position corresponding to at least one of the plurality of laser light detecting means. is there.

[0014]

According to the image forming apparatus of the present invention, the measuring means causes a predetermined clock from the time when one of the plurality of laser light detecting means detects the laser light to the time when the other laser light detecting means detects the laser light. The change of the scanning speed due to the change of the in-machine temperature is detected by measuring the count number of, and the write clock frequency is adjusted by the write frequency correction means so that the measured count number matches or substantially matches the reference count number. By correcting, depending on the change in scanning speed,
Control the write clock frequency.

[0015]

Embodiments of the image forming apparatus of the present invention will be described below in order of [Embodiment 1], [Embodiment 2], [Embodiment 3], [Embodiment 4], [Embodiment 5] with reference to the drawings. The details will be described.

[Embodiment 1] FIG. 1 shows a configuration of a writing unit of an image forming apparatus of Embodiment 1. Laser diode 10
The laser light emitted from No. 1 enters the polygon mirror 102. The polygon mirror 102 has an accurate polygonal shape and rotates in a fixed direction at a fixed speed. This rotation speed is determined by the rotation speed of the photosensitive drum 103, the writing density, and the number of faces of the polygon mirror 102.

The reflected laser light incident on the polygon mirror 102 is deflected by the rotation of the polygon mirror 102. The deflected laser light is reflected by the fθ lens 104.
Incident on. The fθ lens 104 is formed of a plastic lens for the purpose of cost reduction and weight reduction. The scanning light having a constant angular velocity is converted so as to scan the photoconductor drum 103 at a constant speed, and the fθ lens 104 is formed on the photoconductor drum 103. The image is formed so that it becomes the minimum point, and it also has a face tilt correction mechanism.

The laser light passing through the fθ lens 104 is
First, it reaches the position of the first laser light detection sensor 105 arranged outside the image area, then passes through the photosensitive drum 103, and further reaches the position of the second laser light detection sensor 106 arranged outside the image area. Then, they are respectively received. Here, the first laser light detection sensor 105 and the second laser light detection sensor 106 are the laser light detection means of this embodiment, and in particular, the first laser light detection sensor 105 is the laser light scanning synchronization signal ( It also plays a role as a synchronization detection sensor for detecting a synchronization detection signal).

The first laser light detection sensor 105 and the second laser light detection sensor 106 output detection signals DETP1 and DETP2 to the write clock generation circuit 107, respectively, upon receiving the laser light.

In the write clock generation circuit 107, the first laser light detection sensor 105 detects the laser light and the second laser light detection sensor 106 detects the laser light based on the detection signals DETP1 and DETP2. Measure the count number of a predetermined clock up to, compare the measured count number with a reference count number described later, and correct the write clock frequency so that the measured count number is approximately equal to the reference count number. Then, the write clock CLK ₀ is output based on the write clock frequency.

At this time, the write clock generation circuit 1
07 outputs a plurality of clocks having different phases as the write clock CLK ₀ . Further, since the write clock generation circuit 107 corrects the write magnification by generating the write clock, it can be called a magnification correction circuit.

The write clock CLK ₀ output from the write clock generation circuit 107 is input to the phase synchronization circuit 108. Further, the phase synchronization circuit 108 receives the synchronization detection signal (the above-mentioned detection signal DETP1) obtained from the first laser light detection sensor 105 for each scanning of the laser light.

The phase synchronization circuit 108 selects a clock having the closest phase to the synchronization detection signal among the write clocks CLK ₀ composed of a plurality of clocks having different phases, and uses the selected clock as the write clock CLK.
Output to 9.

On the other hand, the laser drive circuit 109 causes the laser diode 101 to emit light in synchronization with the write clock CLK based on an image signal (image data) for forming an image, and outputs laser light.

FIG. 2 shows the configuration of the write clock generation circuit 107, which includes a counter 201 and a flip-flop 202.
-204, control circuit 205, and clock generation circuit 20
6 and. Here, the counter 201 counts the input measurement clock ICLK and is cleared by the detection signal DETP1 of the first laser light detection sensor 105. The flip-flop (DFF1) 202 latches the data of the counter 201 by the detection signal DETP2 of the second laser light detection sensor 106. here,
The latched data (count number) corresponds to the scanning time between the first laser light detection sensor 105 and the second laser light detection sensor 106.

Further, the flip-flop (DFF2) 20
3 and a flip-flop (DFF3) 204 are circuits for synchronizing the timing of latching by the detection signal DETP2 of the second laser light detection sensor 106 with the input clock of the counter 201.

Further, the control circuit 205 sets the / OC signal of the flip-flop 202 from "H" to "L", reads the latched count number, and compares the measured count number with the reference count number. , The write clock frequency is corrected so that the measured count number substantially matches the reference count number.

A clock generation circuit (PLL) 206
Is a plurality of clocks CLK ₀ having different phases at frequencies according to the data output from the control circuit 205.
Is generated and output.

The operation of the above configuration will be described with reference to the configuration of the write clock generation circuit 107 of FIG. 2 and the operation flowchart of the write clock generation circuit 107 of FIG.

First, after the counter 201 is cleared by the detection signal DETP1 of the first laser light detection sensor 105, the measuring clock ICLK is counted by the counter 201 and the detection signal D of the second laser light detection sensor 106 is detected.
The data of the counter 201 is latched by the flip-flop (DFF1) 202 by the ETP2 to measure the scanning time (count number) T1 between the first laser light detection sensor 105 and the second laser light detection sensor 106. Perform (S301).

Next, the control circuit 205 sets the / OC signal of the flip-flop 202 from "H" to "L", reads the latched count number, and determines whether any error occurs during the magnification correction operation. Is determined (S30
2) If an error is detected (when the count number is not normal, etc.), error processing is executed and the content of the error that occurred is notified as a message to the control unit above this operation (S303). , A predetermined write clock frequency (a predetermined reference write clock frequency, a write clock frequency when the write clock is initially adjusted, or a write clock frequency corrected immediately before an error occurs) (S30)
4), the process ends.

On the other hand, when there is no error (when the count number is measured normally), the measured count number T1
Is compared with the reference count number T0 (S305), and it is determined whether the measured count number T1 substantially matches the reference count number T0 (S306). Here, T1≈T0 (T
If 1 and T0 substantially match), the process ends.

The range of T1≈T0 is within the control circuit 20.
Depending on the resolution of the clock generation circuit 206 that generates the write clock based on the correction data of the write clock frequency output from the laser light detection sensor 10
When the write clock is used as the count timing signal for measuring the number of counts between 5 and 106, it is possible to control the write clock frequency with an accuracy equivalent to one clock of the write clock. The range of about ± 1 to ± 5 is set according to the restrictions of 1). Further, by setting T1 = T0 (the measured count number T1 and the reference count number T0 completely match (error 0)) instead of T1≈T0, the correction accuracy of the write clock frequency is improved. Is.

On the contrary, if T1≈T0 is not satisfied, the magnitude relationship between the measured count number T1 and the reference count number T0 is determined (S307). If T1 <T0, the count number T1 is determined.
The write clock frequency is decreased so as to increase (S308), the process returns to step S301, and the first laser light detection sensor 105 and the second laser light detection sensor 1 are again detected.
The scanning time (count number) T1 between 06 and 06 is measured. If T1 <T0 is not satisfied, the write clock frequency is increased so that the count number T1 becomes smaller (S
308), the procedure returns to step S301, and the first laser light detection sensor 105 and the second laser light detection sensor 106 are again used.
The scanning time (count number) T1 between and is measured.

As described above, according to the first embodiment, the optical characteristics of the scanning optical system for converging the scanned laser beam on the image recording surface of the photosensitive drum 103 to form an image are changed due to the environmental changes. It is possible to automatically correct the magnification in accordance with. In addition, as shown in the flowchart of FIG.
A feedback loop (steps S308 and S309 to step S30) is used to control the write clock frequency.
Since it has a loop for returning to 1, it is possible to control the frequency with high accuracy. Further, by storing the correction data at the time of adjusting the initial magnification in the device in advance, it is possible to perform the initial magnification adjustment and the magnification correction over time with the same configuration.

Further, generally, when the scanning time between at least two laser light detection sensors is measured by counting the number of clocks using a counter, when the frequency of the input clock changes, the processing of the number of counts ( Normal / abnormal judgment, correction calculation, etc.) becomes complicated,
In the first embodiment, by setting the frequency of the clock (that is, the measurement clock ICLK) at the time of measuring the reference count number to a certain constant frequency, the processing of the count number is simplified, and the processing of the control circuit 205 is greatly performed. I am trying to reduce it.

In addition, during the magnification correction operation, some error,
For example, if the correction range is exceeded or the scanning time cannot be measured due to damage to the laser light detection sensor and magnification correction cannot be performed, the control circuit 205 detects an error. Then, the correction operation is interrupted, and the predetermined write clock frequency (the preset reference write clock frequency, or the write clock frequency when the write clock is initially adjusted, or the correction immediately before the error occurs in step S304 described above The write clock frequency) is set. The above configuration prevents the device from being unable to form an image,
The device can be operated even during the period until the error that has occurred is resolved. However, this does not apply to errors that make image formation impossible, such as damage to the output means of the synchronization detection signal. In other words, when an error that does not significantly affect image formation occurs during magnification correction, this can be temporarily avoided.

On the other hand, when such an error occurs,
If processing is performed in the write clock generation circuit 107,
The control unit higher than this circuit controls the image forming apparatus in a normal state without recognizing this error. Therefore, if an error occurs,
In the error processing of step S303 described above, the upper control unit responds to the error message by notifying the upper control unit of this operation as a message of the content of the error that occurred, and alerts the operator or the upper system. Is issued, and quick error avoidance can be realized. Further, as described above, it is possible to operate the apparatus without deteriorating the image quality so much until the error is avoided.

Further, the laser light detection sensor used for the purpose of measuring the scanning time is provided once for each main scan for one light source if the laser is turned on at the position of the laser light detection sensor. A detection signal can be obtained. Therefore, as described above, by using the detection signal of the first laser light detection sensor 105 as the synchronization detection signal for the phase synchronization of the writing clock and the generation of the image recording control signal, the scanning time is measured and the synchronization detection signal is detected. Moreover, since the laser light detection sensor can be shared, the structure of the device is simplified, and the number of constituent parts can be reduced, resulting in cost reduction.

The correction of the write clock frequency in the write clock generation circuit 107 can be basically performed at any timing other than the time of image formation. However, since the correction of the write clock (correction of magnification) in the present invention is intended to maintain the image quality against the environmental change of the apparatus, the timing of the write clock frequency correction (setting) can be the timing of image formation. It is desirable to bring them as close as possible. For example, by performing the timing of correcting the write clock frequency when the start button is pressed, the image is formed immediately after the magnification correction, so that high-quality image output is maintained without being affected by environmental changes over time. be able to. Alternatively, you can press multiple images (frames) by pressing the start button once.
In this case, the timing of correcting the write clock frequency is performed between frames during continuous recording to prevent deterioration of image quality due to environmental temperature rise during continuous operation, and It is possible to maintain high quality image output.

[Embodiment 2] Embodiment 2 has the same configuration and operation as Embodiment 1, in which the frequency of the measurement clock ICLK for measuring the reference count number is set to a certain constant frequency. A certain constant frequency is used as a constant write clock frequency.
The processing of the control circuit 105 can be greatly reduced.

A plurality of clocks CLK _{0 having} different phases output from the write clock generation circuit 107 are input to the phase synchronization circuit 108. A synchronization detection signal (detection signal DETP1 of the first laser light detection sensor 105) obtained for each laser scanning is input to the phase synchronization circuit 108, and a plurality of different phases output from the write clock generation circuit 107 are output. The clock having the closest phase to the synchronization detection signal is selected from among the clocks CLK ₀ of 1 to output as the write clock CLK. Therefore, it is possible to obtain a write clock with a small phase error of the clock in each laser scanning (hereinafter, laser scanning (direction) is referred to as main scanning (direction), and a direction orthogonal to the laser scanning direction is referred to as sub-scanning direction).

As described above, the measurement of the scanning time between the laser light detecting sensors for magnification correction is performed by resetting the counter and latching data by a signal synchronized with the main scanning cycle. By using a constant write clock that is substantially synchronized with the main-scan synchronization detection signal as the input clock (ICLK), a counting error due to a phase shift between the detection signal of the laser light detection sensor and the clock is eliminated, and the laser light detection sensor It is possible to measure the scanning time with high accuracy. Further, if the scanning time is measured using the writing clock, for example, even if the recording conditions of the image forming apparatus are changed, it is sufficient to use a constant writing clock according to the recording conditions. Therefore, the control circuit 205 is changed. It is also possible to provide a highly versatile device.

[Third Embodiment] In the third embodiment, in the same configuration as that of the first embodiment, the frequency of the measurement clock ICLK when measuring the reference count number is set to the basic write clock frequency before correction. Is. The basic write clock frequency is determined by the recording conditions of the image forming apparatus.

According to the third embodiment, in addition to the effect of the first embodiment, data relating to a plurality of frequencies (basic write clock frequency data, write clock frequency data upon initial correction, etc.) are controlled. There is no need for management within the circuit 205. Therefore, even if it becomes necessary to make an initial correction again with respect to the change with time of the device, it is sufficient to set the frequency of the measurement clock ICLK for measuring the reference count number to the reference write clock frequency. It is possible to reset easily with a relatively simple structure without being influenced by the correction data of.

[Fourth Embodiment] In the fourth embodiment, in the same configuration as the first embodiment, the count number measured by the counter 201 (measuring means) when the reference clock is initially adjusted for the write clock. It is what

The reference count number used as a reference for frequency control in the write clock generation circuit 107 depends on the interval between at least two laser light detection sensors and the optical characteristics of the optical scanning optical system such as the polygon mirror 102 and the fθ lens 104. If the variation (apparatus difference) between devices or the change in the interval due to deformation over time is small enough to be ignored, it is not necessary to adjust each device, but in reality it is not possible to suppress the variation between devices. It is known that it is difficult and the optical characteristics change due to the temperature change of the device, which affects the output image quality.

On the other hand, in the fourth embodiment, by setting the reference count number to the count number measured when the initial correction is performed, it is possible to set it for each device, and variations in optical characteristics between devices. It is possible to realize the highly accurate magnification correction by avoiding the influence of.

[Embodiment 5] Embodiment 5 has a configuration similar to that of Embodiment 1, and when the write clock generation circuit 107 does not measure the scanning time or the count number between the laser light detection sensors, a plurality of lasers are used. At least one of the light detection sensors (here, two) (here, the second)
The laser is not emitted at a position corresponding to the laser light detection sensor 106).

As described in the first embodiment, the measurement of the scanning time between the laser light detecting sensors necessary for the correction of the writing clock is performed by measuring the scanning time at the time of correction for the purpose of magnification correction. Can be higher. In FIG. 2, the scanning time (the count number of the counter 201) of the two laser light detection sensors is reset by the detection signal DETP1 of the second laser light detection sensor 106 to reset the second laser light detection sensor 106. Since the measurement is performed by latching the counter data with the detection signal DETP2, the detection signal does not need to be input to the circuit of FIG. 2 when it is not necessary to measure the scanning time except during magnification correction. . Therefore, when the scanning time or the number of counts between the laser light detecting sensors is not measured, the laser is not emitted at a position corresponding to at least one laser light detecting sensor required only for measuring the scanning time. If so, the laser does not need to be emitted unnecessarily, and the life of the laser, the photoelectric conversion element used for the laser light detection sensor, the photosensitive material used for image recording, etc. can be extended.

Further, in the configuration of FIG. 2, when the detection signal DETP2 of the second laser light detection sensor 106 is always output (that is, when the laser is emitted at the position corresponding to the laser light detection sensor), If the timing of fetching the measurement result into the control circuit at the same time as the output timing of DETP2 when correcting the write clock,
It is possible that the measurement results may not be captured normally. In such a case, it becomes necessary to control the acquisition timing of the measurement result and perform processing such as synchronizing with the output timing of DETP2. Therefore, in the fifth embodiment, the second laser light detection sensor 1
If the laser is not made to emit light at the position corresponding to 06, the above timing control processing is not necessary and the measurement results can be fetched asynchronously, so that the control circuit can be simplified.

Although the plastic lens is used as the f.theta. Lens 104 in the above-mentioned first to fifth embodiments, even if a general glass lens is used, it is affected by the change of the scanning speed due to the influence of the temperature change. Of course, it is possible to obtain a high-quality image that always maintains the same magnification (precision of zooming) and obtain the same effect. Further, the number of laser light detection sensors is not particularly limited to two, and it is needless to say that the same effect can be obtained by using two or more laser light detection sensors.

[0053]

As described above, in the image forming apparatus of the present invention, one of the plurality of laser light detecting means detects the laser light by the measuring means and the other laser light detecting means detects the laser light. The change in scanning speed due to the change in the temperature inside the machine is detected by measuring the count number of the predetermined clock up to, and the measured count number matches or substantially matches the reference count number by the writing frequency correction means. By correcting the write clock frequency so that
Since the write clock frequency is controlled according to the change in scanning speed, high-quality images that always maintain equal magnification (precision of zooming) are not affected by changes in scanning speed due to the effects of temperature changes. Can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of a writing unit of an image forming apparatus according to a first exemplary embodiment.

FIG. 2 is an explanatory diagram showing a configuration of a write clock generation circuit.

FIG. 3 is an operation flowchart of the write clock generation circuit according to the first embodiment.

[Description of Reference Signs] 101 laser diode 102 polygon mirror 103 photoconductor drum 104 fθ lens 105 first laser light detection sensor 106 second laser light detection sensor 107 write clock generation circuit 108 phase synchronization circuit 109 laser drive circuit 201 counter 202-204 flip-flop 205 control circuit 206 clock generation circuit

Claims (10)

[Claims] 1. An image forming apparatus for writing image information on a photosensitive member using laser light, comprising a plurality of laser light detecting means for detecting laser light moving in a main scanning direction, and the plurality of laser light detecting means. One of the measuring means for measuring the count number of a predetermined clock from the detection of the laser light by the other laser light detecting means to the detection of the laser light by the other laser light detecting means, and the count number measured by the measuring means. An image characterized by comprising: a write frequency correction means for comparing the write clock frequency so that the measured count number matches the reference count number and the reference count number set for Forming equipment. 2. The reference count number is determined by using a timing signal having a certain constant frequency, after one of the plurality of laser light detecting means detects laser light by the measuring means, and then another laser light detecting means. The image forming apparatus according to claim 1, wherein a count number until the laser detects the laser light is set and set. 3. The certain constant frequency is a certain constant write clock frequency.
The image forming apparatus described. 4. The image forming apparatus according to claim 3, wherein the certain write clock frequency is a basic write clock frequency before correction. 5. The image forming apparatus according to claim 1, wherein the reference count number is a count number measured by the measuring unit when the write clock is initially adjusted. 6. The write frequency correction means adjusts the write clock frequency to a predetermined reference write clock frequency or initially adjusts the write clock when an error occurs during the write clock frequency correction operation. 2. The image forming apparatus according to claim 1, wherein the correction operation is completed by setting the write clock frequency set when performing the above or the write clock frequency corrected immediately before the error occurs. 7. The image forming apparatus according to claim 1, wherein a signal obtained from at least one of the plurality of laser light detecting means is used as a laser light scanning synchronization signal. 8. The image forming apparatus according to claim 1, wherein the writing frequency correction unit executes the correction of the writing clock frequency when the start button of the image forming operation is pressed. 9. The image forming apparatus according to claim 1, wherein the write frequency correction unit executes correction of a write clock frequency between frames during continuous recording. 10. The laser does not emit light at a position corresponding to at least one of the plurality of laser light detecting means when the writing frequency correcting means does not measure the count number between the laser light detecting means. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.